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A vacuum-tube device for the generation of pulsed microwave radiation in the submillimeter range (up to 380 GHz) is presented, designed for use as a source in a 360 GHz high-field/high-frequency electron paramagnetic resonance (EPR) spectrometer—the pulsed Orotron. Analogous to the known continuous wave (cw) version, in the pulsed Orotron microwave radiation is generated by the interaction of a nonrelativistic electron beam with a diffraction grating (stimulated Smith–Purcell radiation) in feedback with an open Fabry–Perot resonator construction. The presented design extends the cw Orotron by a gate electrode and a high-voltage pulsing unit to control the electron beam current. The generated pulses at 360 GHz have pulse lengths from 100 ns–10 μs and a pulse power of (22±5) mW. The output in a broader frequency band between 320 and 380 GHz ranges from 20 up to 60 mW. Within a 10 μs time slot, incoherent pulse trains of arbitrary duration can be generated. The pulsed Orotron has been incorporated in the quasioptical microwave bridge of a heterodyne induction mode EPR spectrometer. The first free induction decay measurements at a microwave frequency of 360 GHz and a magnetic field of 12.8 T on a polycrystalline perylenyl–ion sample are presented and future applications and extensions of Orotron-EPR spectroscopy are discussed.

A novel probe head with a two-loop-one-gap resonator for X-band (9.5 GHz) time-resolved transient electron paramagnetic resonance measurements with direct detection is described. The low quality factor Q of the resonator allows time resolution in the order of 10 ns while the high filling factor guarantees a sensitivity which is at least comparable to that of conventional cavity resonators. A novel feature of the resonator is the coupling mechanism which exploits the field distribution in the microwave shield. The type of the resonator and the microwave coupling scheme chosen provide high mechanical stability of the setup. This is particularly important for pulsed laser excitation and gas stream cooling of the sample. The advantages of the probe head are demonstrated by relaxation measurements on the photoexcited triplet state of zinc-tetratolylporphyrin, for which the high time resolution allows the determination of fast anisotropic relaxation. This relaxation behavior can be attributed to the dynamic Jah...

The results of calculations of doublet state G tensors of organic radicals often show unsatisfactory agreement with the respective experimental data. This led us to reconsider the results of the Rayleigh–Schrodinger perturbation theory approach found in the literature. We came to the conclusion that neither the expressions given for restricted nor for unrestricted Hartree–Fock functions are fully correct. In this paper new expressions for the G tensor to be used with restricted Hartree–Fock functions will be introduced and results of calculations employing these new formulas in conjunction with molecular states from semiempirical Hartree–Fock-type calculations are discussed.

Conventional zero-field optically detected magnetic resonance (ODMR) is normally performed by using a slow-wave helix for microwave excitation with a quality factor Q≈1. With available microwave sources this low Q factor leads to long microwave pulse lengths for coherent pulse experiments (π-pulse duration of about 300 ns for 20 W microwave excitation power). For our zero-field experiments we took advantage of the bridged loop-gap microwave resonator configuration with relatively high Q factor. Without the possibility of tuning the Zeeman energy level splitting as in electron paramagnetic resonance (EPR), in zero-field ODMR the resonator has to cover a wide range of frequencies. We are able to tune our probehead in the range of 1.9–8 GHz with a loaded Q factor of up to 800 by using interchangeable bridged loop-gap resonators of various designs. Thereby, the pulse lengths, compared to the slow-wave helix, could be reduced by nearly one order of magnitude (tresonatorπ=45 ns employing the same microwave powe...

Intramolecular electron transfer (ET) in cis and trans isomers of a covalently linked porphyrin–cyclohexylene–quinone, oriented in liquid crystals (LCs), is monitored by time‐domain electron paramagnetic resonance (EPR) spectroscopy over an extended range of temperature, i.e., 210

We present design details of and first measurements with a novel continuous wave (cw) high-field/high-frequency electron paramagnetic resonance spectrometer operating at a microwave frequency of 360 GHz and a magnetic field of up to 14 T. The spectrometer design incorporates a heterodyne mixer detection scheme with a quasi-optical transmission line and a bimodal induction mode Fabry–Perot cavity. First cw experiments on polycrystalline 1,1-diphenyl-2-picryl-hydrazyl and bisdiphenylene-β-phenylallyl benzolate in polystyrene at room temperature and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl in frozen solution at 190 K demonstrate the high Zeeman resolution achievable and allow an estimate of the present detection sensitivity of 4×109 spins/G at a detection bandwidth of 1 Hz.

Electron nuclear triple resonance (TRIPLE) experiments on free radicals in solution not only give considerable signal‐to‐noise improvement as compared to ENDOR, but also decrease the observed linewidth and give additional information about the number of protons contributing to a particular hfs constant. The experimental setup is described and the results are discussed in terms of a phenomenological theory.

The three principal phosphorescent bands of Cr3+ (1%)/tris(acetylacetonato)aluminium(III) single crystals at 1.8 K, have been examined at field strengths of 0–5.7 T in various orientations. The principal g values of the corresponding doublet excited states are determined to lie in the ranges ‖g∥ ‖:1.4–1.7, ‖g⊥ ‖:1.8–2.0, in marked contrast to those of the inorganic analogue, ruby.

First measurements of deuterium quadrupole coupling constants of a polyatomic doublet state radical are reported. The quadrupole couplings were determined by ENDOR and electron–nuclear–nuclear TRIPLE resonance in liquid crystals. For the partially deuterated perinaphthenyl radical the out‐of‐plane component of the deuterium quadrupole coupling was measured to be e2q33Q/h =−(94±3) kHz for both molecular sites. Within experimental error these values are equal to those measured earlier for deuterated alternant hydrocarbons in the diamagnetic singlet ground state.